Array out of bounds, when I try to swap values

I am trying to swap values in a 2D array, but I get an "out of bounds" run time error.

What is wrong?

public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        //Q1
        int row = 3;
        int colum = 5;

        //Declare 2d array
        int [][] matrix = new int [row][colum];
        //Create array and input values
        Scanner input = new Scanner(System.in);
        System.out.println("Enter " + matrix.length + " rows and "
        + matrix[0].length + " colums: \n");
        for (row = 0; row < matrix.length; row++) {
            for (colum = 0; colum < matrix[row].length ; colum++) {
                matrix[row][colum] = input.nextInt();
        }
            }
        System.out.println("\nMultiplication table");
        System.out.println("--------------------");

        //Print the array
        for (row = 0; row < matrix.length; row++ ) {
            for (colum = 0; colum < matrix[row].length; colu开发者_Python百科m++ ) {
                System.out.printf("%4d", matrix[row][colum]);
            }

            System.out.println();
        }
        //Q2 - Make the values swapable
        Scanner input1 = new Scanner(System.in);
        System.out.println("\n1: Modify a value. ");
        System.out.println("0: Exit the application");
        int selection = input1.nextInt();
        switch(selection) {
            case 0:
                System.exit(0);
                break;
            case 1:
                System.out.println("\nPlease enter the row you would like to change: "  );
                Scanner input2 = new Scanner(System.in);
                int changeRow = input2.nextInt();
                System.out.println("You entered: " + changeRow);
                System.out.println("Please enter the colum you would like to change: "  );
                Scanner input3 = new Scanner(System.in);
                int changeColum = input3.nextInt();
                System.out.println("You entered: " + changeColum);

    error--->   int temp = matrix[row][colum];
                matrix[row][colum] = matrix[changeRow][changeColum];
                matrix[changeRow][changeColum] = temp;

                System.out.println("The value in row " + changeRow + "and colum " + changeColum + "is now changed to " + temp);




                break;

            }
        }
    }

---

It would have been easier to spot this if you had posted the stack trace of your exception. Here is my guess:

 int temp = matrix[row][colum];

What are the values of row and column here? They are last used before in the loop to print the array, thus you now have row == matrix.length, and column == matrix[row].length (with the row value one before).

Of course, this is outside of the permissible bounds of the array, and you get your IndexOutOfBoundsException.

---

You are using row and column in your loops. Check the value of them AFTER the loops. I'm not sure if the increment is done and then the < check fails, but if it does, then this

int temp = matrix[row][colum];

is trying to find

matrix[3][5];

and as it starts at 0, that doesn't exists.

---

When you get changeRow, changeColum inputs you need to create another array initialize with lengths and then assign the values by comparing previous array lengths.